I. Definitions of Open-Loop Water Systems and Closed-Loop Water Systems?
① An open-loop water system, also termed an open-circuit water system, utilises water sourced from industrial water that undergoes chemical treatment before entering the various systems of the power plant’s steam turbine boiler via an open-loop water header. This water cools the users of the open-loop water, primarily including:
– Generator hydrogen coolers
– Closed-loop water coolers
– Feedwater pump motor air coolers
– Vacuum pump coolers
– Hydrogen system, hydrogen dryers
– Sealing oil system, Roots vacuum pump, cooling water
Why is it termed an open-loop water system? Because its water enters the induced draft cooling tower through an open-loop water header pipe for open circulation. hydrogen system dryers, and Roots vacuum pump, and cooling water for the sealing oil system. Why is it termed an open system? Because the water enters the induced draft cooling tower via the open water header pipe for open circulation, it undergoes forced ventilation cooling before returning to the system.
② Closed-loop cooling water, also termed the closed-circuit cooling system, utilises chemically treated deionised water as its source. Owing to its superior quality, it serves users with stringent water purity requirements, such as: – Main engine oil coolers – Mechanical seal water and bearing cooling water for feedwater pumps and condensate pumps – Stator cooling water for generator stator cooling systems – Cooling water for boiler coal mill systems Its primary flow path involves water passing through a closed tank, being pressurised by a closed pump, entering a closed water cooler for temperature reduction, circulating through the system to absorb heat at the user point, returning to the closed cooling water tank, and then re-entering the closed pump inlet to repeat the cycle. As the entire process occurs within a sealed environment, it is referred to as a closed water system.
II. What are the principal differences between the two?
1. Their circulation methods differ. Open water systems operate in an open circuit, directly exposed to air, resulting in evaporation losses that necessitate continuous replenishment of substantial water volumes. Compared to other options, they offer superior heat exchange efficiency. Closed water systems, conversely, circulate within a sealed circuit, eliminating evaporation losses. Aside from leakage, the water volume remains constant, requiring only minimal external supplementation and incurring lower water consumption losses.
2. Water quality differs. Open-loop systems utilise lower-grade industrial water, suitable for cooling applications with minimal water quality requirements. They demand substantial flow rates but operate at lower pressures. Closed-loop systems, supplied by demineralised water, cater to users with stringent water quality specifications.
3. Parametric differences.
Pressure in open-loop systems typically ranges from 0.2 to 0.25 megapascals (MPa), whereas closed-loop systems can achieve pressures of 0.5 to 0.6 MPa.